MDEV-11335 Changing delay_key_write option for MyISAM table should not copy rows

Don't rebuild the table for ALTER TABLE delay_key_write changes.

After that, delay_key_write value in .frm may differ from the
value in .MYI. We'll do what .frm says.

mysql-test/r/alter_table_online.result

@@ -184,6 +184,35 @@ CREATE TABLE t1 (a LONGTEXT COLLATE latin1_general_ci);
 ALTER TABLE t1 MODIFY a LONGTEXT COLLATE latin1_swedish_ci, ALGORITHM=INPLACE;
 ERROR 0A000: ALGORITHM=INPLACE is not supported for this operation. Try ALGORITHM=COPY.
 DROP TABLE t1;
-#
-# End of MDEV-8948 ALTER ... INPLACE does work for BINARY, BLOB
-#
+select @@global.delay_key_write;
+@@global.delay_key_write
+ON
+create table t1 (a int, b int, key(b));
+flush tables;
+flush status;
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	0
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	0
+alter online table t1 delay_key_write=1;
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	1
+flush tables;
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	2
+alter online table t1 delay_key_write=0;
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	2
+flush tables;
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+Variable_name	Value
+Feature_delay_key_write	2
+drop table t1;

mysql-test/t/alter_table_online.test

@@ -285,6 +285,24 @@ CREATE TABLE t1 (a LONGTEXT COLLATE latin1_general_ci);
 ALTER TABLE t1 MODIFY a LONGTEXT COLLATE latin1_swedish_ci, ALGORITHM=INPLACE;
 DROP TABLE t1;
 
---echo #
---echo # End of MDEV-8948 ALTER ... INPLACE does work for BINARY, BLOB
---echo #
+#
+# MDEV-11335 Changing delay_key_write option for MyISAM table should not copy rows
+#
+select @@global.delay_key_write;
+create table t1 (a int, b int, key(b));
+flush tables;
+flush status;
+show status like 'Feature_delay_key_write';
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+alter online table t1 delay_key_write=1;
+show status like 'Feature_delay_key_write';
+flush tables;
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+alter online table t1 delay_key_write=0;
+show status like 'Feature_delay_key_write';
+flush tables;
+insert t1 values (1,2),(2,3),(3,4);
+show status like 'Feature_delay_key_write';
+drop table t1;

storage/myisam/ha_myisam.cc

@@ -825,6 +825,10 @@ int ha_myisam::open(const char *name, int mode, uint test_if_locked)
   /* Count statistics of usage for newly open normal files */
   if (file->s->reopen == 1 && ! (test_if_locked & HA_OPEN_TMP_TABLE))
   {
+    /* use delay_key_write from .frm, not .MYI */
+    file->s->delay_key_write= delay_key_write_options == DELAY_KEY_WRITE_ALL ||
+                             (delay_key_write_options == DELAY_KEY_WRITE_ON &&
+                       table->s->db_create_options & HA_OPTION_DELAY_KEY_WRITE);
     if (file->s->delay_key_write)
       feature_files_opened_with_delayed_keys++;
   }
@@ -2269,10 +2273,8 @@ bool ha_myisam::check_if_incompatible_data(HA_CREATE_INFO *create_info,
       table_changes & IS_EQUAL_PACK_LENGTH) // Not implemented yet
     return COMPATIBLE_DATA_NO;
 
-  if ((options & (HA_OPTION_PACK_RECORD | HA_OPTION_CHECKSUM |
-		  HA_OPTION_DELAY_KEY_WRITE)) !=
-      (create_info->table_options & (HA_OPTION_PACK_RECORD | HA_OPTION_CHECKSUM |
-			      HA_OPTION_DELAY_KEY_WRITE)))
+  if ((options & (HA_OPTION_PACK_RECORD | HA_OPTION_CHECKSUM)) !=
+      (create_info->table_options & (HA_OPTION_PACK_RECORD | HA_OPTION_CHECKSUM)))
     return COMPATIBLE_DATA_NO;
   return COMPATIBLE_DATA_YES;
 }